Over-pressure valve for liquid circuit interrupter



Nov. 23, 1954 B. P. BAKER ETAL 2,695,349

OVER-PRESSURE VALVE FOR LIQUID CIRCUIT INTERRUPTER Filed July 31, 1951 2 Sheets-Sheet l .2. Fig. I.

Insulation Fig. 3.

INVENTORS Benjamin P. Baker 8 Wayne 8. Aspey.

Nov. 23, 1954 B. P. BAKER ETAL 2,695,349 OVER-PRESSURE VALVE FOR LIQUID CIRCUIT INTERRUPTER Filed July 51, 1951 2 Sheets-Sheet 2 Fig.4.

n WITNESSES: INVENTORS Ben] n P. Baker and 54%, W e S Aspey.

2,595,349 Patented Nov. 23, 1954:

.tiice OVER-PRESSURE VALVE FOR LIQUED CIRCUIT INTERR UPTER Benjamin R. Baker and Wayne 5. Aspey, Turtle Creek, Pa., assignors to Westinghouse Electric Corporation, East Pittshnrgh, Pa., a corporation of Pennsyivania Appiication July 31, 1951, Seriai No. 239,462 1%) Claims. (Ci. 26il--i5ii) This invention relates to circuit interrupters in general, and, more particularly, to overpressure exhaust valves for the arc-extinguishing structures of liquid-break circuit interrupters.

A general object of our invention is to provide an improved circuit interrupter of the liquid break type which wiil give improved and more eifective operation, particulariy during two or more rapid'reclosing operations.

Another object is to provide an improved over-pressure valve arrangement for a liquid break circuit interrupter in which the exhaust gases will be diffused and dispersed when they are exhausted, thereby eliminating the possibility of subjecting adjacent parts of the interrupter to a concentrated blast of hot gases.

Anotherobject is to provide an improved liquid break circuit interrupter in which the overpressure exhaust valve is so disposed with relation to the liquid inlet valve that the exhaust'gases are more rapidly expelled from the interrupter.

Another object is to provide an improved relief valve construction for a circuit interrupter in which'the arc' gases are rapidly removed from the vicinity of the pressure-generating contacts, so that during subsequent opening operations, in. rapid order, said pressure-generating contacts will open in liquid, such as oil,.and not in gas.

Another object is to provide an improved over-pressure exhaust valve arrangement for a circuit interrupter in which th'eexhaust gases are exhausted in opposite directions so as to balance the reaction forces of the jets of gas from. the exhaustsand to provide an improved valve spring arrangement whereby the two cooperating overpressure valves will open at the same pressure.

Further objects and advantages will readily become apparent upon reading the following specification taken in conjunction with the drawings, in' which:

Figure l is a side elevational view, partially in'vertical section, of a circuit interrupter embodying -our invention and shown in the closed circuit position;

Fig. 2 is an enlarged vertical sectional view through the left-hand arc-extinguishing unit of Fig; 1, the contact structure being shown in the closed circuit position;

Fig. 3 is an'enlarged vertical sectional view through: the intermediate contact of the. interrupter of Fig. 2, taken along the line III-III of Fig. 2,'looking in the direction of the arrows;

Fig. 4 is an enlarged vertical sectional view taken through the contact foot of the interrupter, theview being taken substantially along theline- IVIV of Pig. 2;

Fig. 5 is a horizontal sectional view through a spring seat of our overpressure valve arrangement;

Fig. 6 is a'horizontal sectional view through the overpressure valve of our improved over-pressure valve 'ar rangement;

Fig. 7 is an enlarged broken vertical sectional view, taken substantially along the line VlI--VII of Fig. 8;

Fig. 8 is an end elevational View of the oil inlet valve construction of Fig. 7; and,

Fig. 9 is a schematicview cipies of our invention.

In multiple orifice and similar type interrupters for oil circuit breakers, the pressure-generating compartment has been provided with over-pressure relief valves and inlet valves. These valves have functioned to prevent build-up of excessive pressures and permit gasto escape after each operation and before the succeeding operation. These valves were eitherlocated in the same place at the top of the pressure-generating cell casting or the relief valve was illustrating some of the prinon the side of the casting and below the inlet valve. This construction permitted satisfactory operation at relativeiy high currents, single opening operations and single reclosures. In order to handle heavier short circuit currents corresponding to 10 million kv.-a. at 161 and 138 kv. and multiple high speed reclosures, it has been found necessary to solve certain problems, which has been done by the improvements constituting the subject matter of the present invention.

Referring more particularly to Fig. l, the reference numeral 1 designates a tank filled to the level 2 with an arc-extinguishing liquid 3, in this instance, circuit breaker oil. Depending from the cover 4 of the tank 1 are two terminal bushings 5, 6, to the lower ends of which are app i arc-extinguishing units 7, 3.

Eiee' lcally interconnecting the arc-extinguishing units '7, ii, and operating the same, is a conducting crossbar 9 vertically actuated in a reciprocal manner by an insulating iit't rod The lift rod 10 is actuated by any suitable n'rechanism, which forms no part of our invention. This :iechanism, however, may be of the modern type in which two, three or more rapid reclosing operations take place in quick succession. Thus such reclosing operations are made to take place in the hope that should a fault exist on the line connected to, and protected by, the circuit i terrupter, the fault may be of a temporary nature, and a during a subsequent reclosing operation, the fault by this time, have been removed so that normal exti guishing unit 7 of Fig. 1. Referring to Fig. 2, it will be coserved that threadedly secured to the terminal stud Ill extending interiorly through the left-hand terminal 5, is a contact foot 12. The contact foot 12 has ted clamping portion 13, interiorly threaded to l arch the threads at the lower end of the terminal stud ii, and a clamping bolt 14 extends through apertures 15 provided at the extremities of the two legs of the bifurcated clamping portion 13 to clamp the contact foot 12 fixedly in position once adjustment has been made.

The contact foot 12 is secured by three triangularly disposed bolts 16 to a top dome casting 17 which defines a pressure-generating chamber 18. Within the pressuregenerating chamber 18 a movable hook-shaped pressuregenerating contact 19 separates upwardly away from an intermediate contact, generally designated by the reference character 2-9, to establish a pressure-generating arc therebetween.

Cooperable with the intermediate contact 20 is a lower movable interrupting contact 21 having a lower cap portion 22. which serves as a lower seat for a battery of accelerating compression springs 23, more clearly shown in Fig. 2.

The left-hand end 24 of the conducting cross-bar 9 strikes the lower end of the cap portion 22 of the lower movable interrupting contact 21 and moves the same upwardly during the closing operation, in opposition to the biasing action exerted downwardly by the battery of compression springs 23. The end 24- of the cross-bar 9 also strikes an insulating side operating rod 25, which is biased downwardly by an accelerating compression spring 26, the latter seating upon a washer 27 resting upon nut 28 threadedly secured to the lower metallic threaded portion 29 of the operating rod 25.

The upper end of the side operating rod 25 has a slot 25:: therethrough, through which passes a pivot pin 99. The pin 9% passes, with slight clearance, through a movable spring housing 91, enclosing a compression spring 91a, and also through the upper ends of two links 92 disposed on opposite sides of the spring housing 91. The lower of the links 92 are pivotally secured, as at 93, to two actuating arms The actuating arms 94 are part of an inte ral casting including the pivot shaft 95 and the pressure-generating Contact 19.

Thus upward movement of side operating rod 25 will close the pressure-generating contact 29, through the compression spring 910 and pin 99 moving down slightly in slot 25a of rod 25. Downward movement of side operating rod 25 will first effect engagement of pin 9% with the upper end of slot 25:: of rod 25 to initiate movement of the contact 19. Further downward movement of rod will, through the linkage, effect clockwise opening motion of pressure-generating contact 19.

The separation of the lower movable interrupting contact 21 from the intermediate contact 2% draws an interrupting arc, not shown, within an interrupting chamber, generally designated by the reference numeral in Fig. 2. This interrupting chamber 311 is defined by a plurality of superimposed suitably configured insulating plates forming collectively a plurality of orifices 31, through which the rod-shaped movable interrupting contact 21 passes. A plurality of pairs of inlet passages 32 are also defined by the plate structure, and these pairs of inlet passages connect with two vertical flow passages, generally designated by the reference character 33, and hydraulically interconnecting the pressure-generating chamber 18 with the interrupting chamber 30.

The particular features of the passage arrangement defined by the plate structure form no part of our invention, and reference may be had to U. S. Patent No. 2,467,760, issued April 19, 1949, to Leon R. Ludwig, Benjamin P. Baker and Winthrop M. Leeds, and assigned to the assignee of the instant application, for a full description of the details of the plate arrangement, together with a full explanation of the theory of arc interruption.

For our purpose, it is merely necessary to know that liquid under pressure generated within the pressure-generating chamber 18, by the drawing of the pressure-generating are between contacts 19, 20, passes downwardly through the vertical flow passages 33 and through the several pairs of inlet passages 32 to strike the interrupting arc, drawn between the contacts 20, 21 through the orifices 31. The oil, after passing through the orifices 31, is eXhausted out of the extinguishing unit 7 through a plurality of pairs of exhaust passages 34 indicated in Pig. 2. For a full description of the configuration of the exhaust passages 34, reference may be had again to the aforesaid Patent 2,467,760.

The plate structure is mounted upon insulating tie-rods 35, and compression springs 36, encircling the tie-rods 35 serve to compress the several plates together under a suitable pressure.

Disposed at the lower end of the arc-extinguishing unit 7 is a cylindrical piston member 37, picked up during the opening operation, after a predetermined time delay, by an actuating ring 38, disposed interiorly within the cylindrical piston member 37, and serving as a lower seat for a piston compression spring 39. This time delay is described and claimed in United States patent application filed December 15, 1943, Serial No. 514,366, now U. S. Patent 2,592,635, issued April 15, 1952, to Winthrop M. Leeds, Robert E. Friedrich and Francis J. Fry, and assigned to the assignee of the instant application. Thus, during the opening operation, the piston 37 remains stationary until a shoulder 40, or externally extending flange portion, on the actuating ring 38 strikes an inwardly extending flange portion 41 of the piston 37, at which time the piston 37 moves downwardly with the actuating ring 38 to create pressure within a piston chamber 42.

The piston chamber 42 hydraulically interconnects through passages, not shown, with the interrupting chamber 36 so that during low current interruption, or during the interruption of charging currents of relatively low amperage, where the pressure generated within the pressure-generating chamber 18 is weak. at this time liquid will flow upwardly from the piston chamber 42 into the interrupting chamber 30 to effect extinction of the interrupting arc therein.

Preferably, an inlet valve 43, or one-way acting flap valve, is provided to close upon the downward working stroke of the piston 37, and to open during the closing operation of the interrupter, at which time the piston 37 moves upwardly with the cap 22 of the lower interrupting contact 21. Obviously, the returning upward stroke of the piston 37 tends to cause cavitation within the piston chamber 42, and at this time the inlet valve 43 will open to permit the drawing of fresh oil into the piston chamber 42 in readiness for the subsequent opening operation.

Substantially atmospheric pressure exists upon the top, or non-working side, of the piston 37 by virtue of ports 44 leading to the region exteriorly of the unit 7. These ports 44 are simply slots provided in the lower plates 45 and collectively provide a passage to the outside of the unit 7. Since atmospheric pressure exists on the rear side of the piston 37, it will be inoperable during high current interruption when high pressure exists within the extinguishing unit 7. Thus, this high pressure existing during high current interruption, will prevent downward working motion of the piston 37 under the influence of piston spring 39, so that at this time the interrupting contact 21 will move downwardly with the cross-bar 9 separating from the actuating ring 38 and piston 37. Following a subsidence of the pressure within the unit 7 following circuit interruption, the piston 37 will then move downwardly and provide a flushing flow of liquid into the interrupting chamber 30.

Fig. 3 shows, on an enlarged scale, a cross-sectional view through the stationary intermediate contact 20 of Fig. 2. It will be observed that there is provided a pair of cooperating contact fingers 46, the upper ends 47 of which engage the pressure-generating contact 19, and the lower ends 48 of which engage the upper end of the lower movable interrupting contact 21. The contact fingers 46 are retained, and guided, by a stationary key or shaft 49. Compression springs 50 are provided to bias the contact fingers 46 inwardly into good contacting engagement with the pressure-generating and movable interrupting contacts 19, 21, respectively, when the breaker is in the closed contact position. When in the open contact position, contact fingers 46 are retained in their proper position by stationary key 49.

As shown in Fig. 3, the contact fingers 46 and compression springs 50 are encased within a cylindricallyshaped casing 51 having two grooved portions 52, which serve, in cooperation with an insulating bifurcated member 53, to maintain the intermediate contact 20 in a stationary position. Certain features of the intermediate contact 20 are set out and claimed in United States patent application filed April 15, 1950, Serial No. 156,093, now U. S. Patent 2,600,211, issued June 10, 1952, to George B. Cushing and assigned to the assignee of the instant application.

Referring to the pressure-generating chamber 18, it will be observed that the top dome casting 17 has a lateral opening 54 which is closed by a cover plate 55. The cover plate 55 may be secured by bolts 56 to the top dome casting 17. As more clearing shown in Figs. 7 and 8, the cover plate 55 has apertures 57 to accommodate the bolts 56. The cover plate 55 also has an enlarged opening 58, which serves as an inlet opening and is valvecontrolled by a valve plate 59.

The valve plate 59 is mounted upon four bolts 60, the shank portions 61 of which extend through apertures 62 provided in the cover plate 55. The cover plate 55 is reamed out in registry with the apertures 62 to accommodate compression springs 63, which serve to bias the valve plate 59 toward the right, as viewed in Fig. 7, in an opening direction away from the inlet opening 58.

Encircling the shank portions 61 of the bolts are elongated washers 64 having outwardly extending flange portions 65 at their right hand ends, as viewed in Fig. 7, the flange portions serving as the right-hand seats for the compression springs 63. The washers 64 assist in guiding the valve plate 59 to its closed position, at which time it covers the inlet opening 58.

Below the inlet valve 59 in an arcing horn 66 secured by bolts 67 to the cover plate 55. The upper end of the pressure-generating arc will transfer from the lower tip of the movable pressure-generating contact 19 to the are horn 66 during the opening operation to thereby prevent excessive lengthening of the pressure-generating arc.

Referring to Fig. 2, it will be noted that the top dome casting 17 is apertured, as at 68, to lead into a vertically-extending chimney, or cupola portion, 69 of contact foot 12, the upper end of said cupula portion 69 terminating at its upper end into two opposed exhaust passages 70 and 71 (Fig. 4).

Referring to Fig. 4, it will be noted that the exhaust passages 70, 71 are valve-controlled by a pair of overpressure exhaust valves 72, each of which is more clearly shown in Fig. 6 of the drawings. An aperture 73 is provided through each exhaust valve 72 to accommodate a mounting bolt 74. Encircling the mounting bolts 74 are a pair of over-pressure valve springs 75 which have as their function the maintenance of the over-pressure valves 72 in their closed position, closing the exhaust passages 70, 71. The inner ends of the valve springs 75 seat upon a shoulder portion 76 of the exhaust valves 72,

portion 77 of a pair of cup-.rashers 78..(Fig. 5), which partiallyenclose nuts 79 :threadedly securedto the ends of the mounting bolt 74.

The mounting bolt 74- loosely extends through a bore 80'provided in thecontact foot 12.- To insure that both over-pressure valves. 72. will open initially at the same internal pressure within the contact foot 12, the nuts 7? are: screwed up until a certain distant D exists between theouter side. face of the. over-pressure valves 72. In. a particular instance, the distance D .was 2 inches. When this distance D exists at :both ends of the exhaust valve arrange ment, an aperture 81 is bored downwardly throughthe contact foot casting 12, and also through the bolt'74. A locking pin 82. is then inserted through the bore 32, and

the contact foot casting 12 is .peened over to hold lock'- ing pin 82 I permanently in place.

It will be apparent from the foregoing adjustment that in a state of equilibrium of the mounting bolt 74 equal axial. thrust forces F, F exist against the nuts 7?. Also equal inward forces 7, f" are. exerted by the sprirrs it? upon the valves 72. Consequently, after the'foregoing adjustment has been made, and the pin 82 has been in sorted through the bore 81, the over-pressure valves 72 are initially opened at the same internal gas pressure. However, any further opening of the valve 72 will depend upon the characteristics of thevalve springs 75, which may vary slightly from spring to spring. the time of initial opening of the valves-72 is important, and the foregoing. adjustment ensures that both valves will open initially at the same internal pressure P within the casting 12, so that the reactive forces exerted upon the unit 7 will be equalized by the simultaneous opening of the two over-pressure valves 72.

To illustrate the principle of operation of certain as pects of our invention regarding positions of inlet valves 59 and relief valves 72, reference may be had to Fig. 9. Fig, 9 represents a transparent container 33 which is filled with a liquid, such as oil 84. inside of this container is a second container-85 with an opening at the top, which represents openings 7% and 71 of Fig. 4, and an opening at the bottom representing 58 of Fig. 2. As sume container 85 to be partially filled with a gas 85. The pressure head X-l-H above the opening 58 will determine the pressure p on the gas at 87; however, the pressure head H will determine the difference of pressure p inside and p outside of 85 at the opening 7a) or 71, and therefore the greater H, the greater the rate of expulsion of gas 86.

Consequently, referring to Figs. 2 and 4, it will be observed that the height of the chimney or cupola between the inlet opening 58 and the exhaust openings 7t), 7?. is considerable. This brings about a situation in which a considerable head of liquid H, measured from the level of outlet opening 70 and 71 (Fig. 4) to the top of liquid level 2 (Fig. 2), is present to effect an exhausting of the gas column within cupola 69.

The advantages of our invention are numerous. This results from moving the over-pressure exhaust valve 72 to a higher elevation than previousiy employed and discharging the gases in two vertical planes, and also providing the passages 70, 71, 180 apart. The inlet vent 58 has been lowered, as indicated in Fig. 2, and located as much below the over-pressure vents 7 0, 71 as possible. Two small holes 88 (Fig. 4) were placed at the extreme top of the gas cell or cupola. 69 for the same reason as previously explained, and arranged to communicate with the gas bubble outside of the unit 7, which is produced by the exhaust from the over-pressure vents 70, 71. The following advantages are readily apparent:

1. The exhaust from the over-pressure vents 7 9, 71 is raised to the top of the upper static shield 89, and thus decreases the bursting forces on the shield 89, which caused damage when it was burned down in the poorly vented regions.

2. The vents 76-71 are divided and located at 180 in a horizontal plane, and made to discharge in two vertical circles. The exhaust gas is thus diffused over a considerable area, and all rocketing reactions are balanced by the double-exhaust-valve arrangement.

3. The overpressure vents 70, 71, being located in the top of the contact foot casting 12, result in the passage 69 leading to them being as long vertically as possiface of the cup. Washers 73 and the. inner- Nevertheless,

. communicate with gas bubbles at both ble and forming a vertical. cupola. This cupola. 69 quickly gathers all the gas in the pressure chamber; 18",. conducting it away from the. pressure-generating. arc, the inlet vent 5S: and the oil passages 33 leading; into theinterrupting chamber 30'. This allows vthepressure are on succeeding and closely spaced interruptions to be; drawn in'oil rather than in a gas bubble, thereby insuring that no gas is blown into the interrupting are, and places the gas from a given interruption in a position where it, and not oil, is discharged by the followinginterruption. Thus the third and following interruptions are duplicates: of the second.

4. The small holes 88 in the top of the venting cupola 69 permit very little. discharge of oil. However, if they ends theyare'capable oftransmitting gas very rapidly with small pressure. gradients. Therefore, these holes 88 interfere very little: with normal operation, but following aheavy. fault the pressure head caused by the elongated gas bubble in-the. cupola 69perrnits rapid flow of gas from the. gas bubble: inside to the gas bubble outside, which resulted from the operation of the over-pressure'valves 72. Also, the inlet vent 58 being below these holes 88 allows oil to flow in rapidly due to the mobility of the escaping gas through these holes 88.

It will be readily apparent that by our improved inlet valve arrangement and over-pressure exhaust-valve construction, we have greatly improved effective operation of circuit interrupters of the liquid-break type in whichtwo or more rapid reclosing' operations take place. The structurewadds little in :the way of cost and gives remarkably eifective operation.

Although we have shown and described a specific structure, it is to be clearly understood that the same was merely for thepurpose of illustration and that changes. and modifications may be readily made therein by those skilled in the art without departing from the spirit and" scope of the appended claims.

We claim as our invention:

1. A circuit interrupter including meansdefining a pressure-generating chamber submerged in an arc-extinguishing liquid, means for establishing a pressure-gencrating arc. within the pressure-generating chamber, an overpressure relief valve disposed in a wall of the pressure-generating chamber, an inlet valve disposed in a Wall of the pressure-generating chamber, and the overpressure relief valve being disposed at a greater vertical height than the inlet valve.

2. A liquid break circuit interrupter including a tank containing an arc-extinguishing liquid, a terminal bushing extending into the tank, a contact foot secured to the interior end of the terminal bushing, an arc-extinguishing unit supported by the contact foot and including a pressure-generating chamber, the contact foot having an interiorly disposed region freely communicating with the pressure-generating chamber but extending upwardly therefrom, overpressure relief valve means supported at the upper end of the interiorly disposed region and controlling the pressure within said interiorly disposed region, and means providing substantially oppositely disposed exhaust passages associated with the relief valve means.

3. A circuit interrupter including means defining a chamber submerged in an arc extinguishing liquid, means for establishing an are within the chamber, overpressure valve means including a pair of exhaust passages extending in substantially opposite directions out of the chamber, an overpressure relief valve for closing each exhaust passage, a mounting bolt encircled by the overpressure relief valves, a pair of biasing springs encircling the mounting bolt and biasing the valves to their closed positions to thereby exert tension on the mounting bolt, and means securing the mounting bolt fixed in position.

4. A circuit interrupter including means defining a pressure-generating chamber submerged in an arc extinguishing liquid, means for establishing a pressure-generating are within the pressure-generating chamber, overpressure valve means including a pair of exhaust passages extending in substantially opposite directions out of the pressure-generating chamber, an overpressure relief valve for closing each exhaust passage, a mounting bolt encircled by the overpressure relief valves, a pair of biasing springs encircling the mounting bolt and biasing the valves to their closed positions, and a pair of adjustable spring seats also supported upon the mounting bolt at'the oppo-' site ends thereof.

5. A circuit interrupted including means defining a pressure-generating chamber submerged in an arc-extinguishing liquid, means for establishing a pressure-generating are within the pressure-generating chamber, an inlet valve disposed adjacent the lower end of said pressure-generating chamber, said pressure-generating chamber defining a long vertically extending cupola for the exhausting of gas, and overpressure valve means disposed at the extreme upper end of the cupola.

6. A circuit interrupter including means defining a pressure-generating chamber submerged in an arc-extinguishing liquid, means for establishing a pressure-generating arc within the pressure-generating chamber, an inlet valve disposed adjacent the lower end of said pressure generating chamber, said pressure-generating chamber defining a long vertically extending cupola for the exhausting of gas, and overpressure valve means disposed at the extreme upper end of the cupola, said overpressure valve means including a pair of oppositely disposed valve controlled exhaust passages.

7. A circuit interrupter including means defining a pressure-generating chamber submerged in an arc-extinguishing liquid, means for establishing a pressuregenerating are within the pressure-generating chamber, an inlet valve disposed adjacent the lower end of said pressure-generating chamber, said pressure-generating chamber defining a long vertically extending cupola for the exhausting of gas, overpressure valve means disposed at the exereme upper end of the cupola, and a gas bleeder hole through the wall of the pressure-generating chamber positioned very closely to said overpressure valve means.

8. A circuit interrupter including means defining a pressure-generating chamber submerged in an are extinguishing liquid, means for establishing a pressure-generating are within the pressure-generating chamber, overpressure valve means including a pair of exhaust passages extending in substantially opposite directions out of the pressure-generating chamber, an overpressure relief valve for closing each exhaust passage, a mounting bolt encircled by the overpressure relief valves, a pair of biasing springs encircling the mounting bolt'and biasing the valves to their closed positions, a pair 'of adjustable spring seats also supported upon the mounting bolt at the opposite ends thereof, the biasing springs being compressed the same amount, and means for fixedly securing the mounting bolt.

9. A liquid break circuit interrupter including a tank containing an arc-extinguishing liquid, a terminal bushing extending into the tank, a contact foot secured to the interior end of the terminal bushing, an arc-extinguishing unit supported by the contact foot and including a pressure-generating chamber, the contact foot providing a vertically extending cupola freely communicating adjacent the lower end thereof with the pressure-generating chamber, overpressure relief valve means disposed adjacent the upper end of said cupola and controlling the pressure therein, and an inlet valve disposed in the wall of the pressure-generating chamber and positioned below the overpressure relief valve means.

10. A circuit interrupter including means defining a pressure-generating chamber submerged in an arc-extinguishing liquid, means for establishing a pressure-generating are within the pressure-generating chamber, an overpressure relief valve disposed in a Wall of the pressure-generating chamber, an inlet valve disposed in a wall of the pressure-generating chamber, the overpressure relief valve being disposed at a greater vertical height than the inlet valve, and a gas bleeder hole through the wall of the pressure-generating chamber positioned very closely to the overpressure relief valve.

References Cited in the file of this patent UNITED STATES PATENTS 

